Process for removing acid components from hydrocarbon distillates



Patented Apr. 4, 1939 UNITED STATE-S 2,152.7;3 rr t cnss FOR REMOVING ACID comro- NTS rnou urns David Louis Yabrofl, Berkeley, Calif maooaanon imam.-

"amt cisoo to Shell Development Company; CaliL, a corporation of No Drawing.

Applicat sesame 1.19:7.

This invention is a continuation-in-part of my co-pending application Serial No. 102,892, filed September 28, 1936, and deals with the removal of weakly acid reacting organic substances from 5 solutions in certain water-insoluble organic liquids by extraction with aqueous solutions or caustic alkali containing a solubility promoter for these substances, and more particularly deals with the removal of mercaptans from hydrocarbon distillates.

It is frequently necessary to eliminate small quantities of organic relatively weak acid reacting components such as mercaptans', phenols, thio-phenols, alkyl phenols, fatty acids, etc.. from their solutions in neutral or weakly basic reacting organic liquids,.which are substantially immiscible with water such as the liquid hydrocarbons derived from petroleum, benzene, toluene, xylene, substituted normally liquid hydrocarbons which :3 are substantially insoluble in water, for instance, chlorinated hydrocarbons, of which chlorethane, ethylene dichloride, trichlorethylene, carbon tetrachloride, chlorpropane, chlorbutylene, chlorbenzene, brombenzene, are examples; or nitrohydrocarbons, for example, nitroethane, nitrobenzene; or other nitrogen containing hydrocarbons such as amyl or higher amines, aniline, wa-

' ter insoluble pyridine derivatives, petroleum bases, etc.

1;? In order that the water-insoluble organic liquids may be treated by my process they must be substantially inert and resistant to chemical reaction with strong aqueous solutions of caustic alkali when contacted therewith for short periods of time, c. g., aboutlO minutes or less at normal room temperatures.

My invention comprises extracting organic acids which are diflicult to extract such as the weak acids having dissociation constants lower 40 than those of fatty acids, e. g., mercaptans, phenols, etc., contained in water-insoluble organic liquids which are substantially in rt toward strong aqueous caustic alkali solutions at normal room temperatures, with an aqueous solution of caustic alkali in which :is dissolved a substantial amount of an aliphatic amino alcohol, under conditions to absorb at least a major portion of the weak organic acids in the aqueous solution, and toform two layers :and separating the layers.

In the application Serial No. 1021392, filed September 28, 1936, I have disclosed that certain polar substances which are at least partly miscible with aqueous solutions :.of strong caustic alkali, promote the solvent power for weakorgaric acids of aqueous caustic alkali solutions "in which they are dissolved. IIhaveshown that among other I compounds, aminoalkyl amines and hydroxy alkylamines in which the alkyl group contains 2 or 3 carbon atoms arehighly effective in the matter ethanol amines, and propanolamines. Oi these io the mono ethylene diamine, mono ethanol amine and the mono propanol amines are most useful.

Now I have discovered that diamino alkanols of 3 to 5 carbon atoms, namely the diamino propanol, diamino isopropanol, primary, secondary m and tertiary diamino butanolsand diamino pntanols, are equally and more effective in promoting the solubility of weak organic acids in aqueous caustic alkali solutions. These diamino alkanols are miscible with strong aqueous caustic alkali solutions, and at the same. time are little soluble in water-insoluble organic liquids, and in particular in liquid hydrocarbons. 'Diamino alkanols of 6 and more carbon atoms are unsuited because they are insufliciently soluble in strong aqueous caustic alkali solutions and excessively soluble in water-insoluble organic liquids.

For example, when extracting mercaptans from alight gasoline distillate boiling up to 100 0. produced by distillation of a California crude, 5 .oil in a single stage with 10% by volume oi a' 2% normal caustic soda solutions in which have been dissolved 50% of diflerentsolubility promoters, the following results were obtained:

Percent mer- Solubility promoter captans extracked None.- Ethanolamine i312 lDiamino isopropanol 85. 2 Diamino tertiarybutanol. -94. 7

, Aqueous solutions of various caustic alkalis may be used. The alkali metal hydroxides are most 46 useful and eflective although ammonia, alkaline earth hydroxides, quaternary ammonium bases, metal carbonates, etc., may also be suitable.

The concentration of the aqueous caustic alkali may vary within widelimits. fer to use caustic'alkalisolutions which are above about 2 normal andpre'terably between 4 to 10 normal in the absence of the solubility promoter although lower concentrations may be used.

Concentration oi the diamino'alcohols in the 66- In general I pre ably kept between and 60 0., the extraction efiiciency decreasing with increases in thetemperature; and at temperatures below about 0 C. difliculties are frequently encountered due to precipitation of a portion of the solubility promoter and/or excessive viscosity of the aqueous caustic alkali containing the solubility promoter.

The extraction of the organic acids from their solutions in the organic liquids described before may be carried out'bysimply mixing the solution with a predetermined amount of the aqueous caustic alkali solution in which is dissolved a substantial amount of the diamino alkanol, and then separating the liquids. The resulting aqueous solution contains most of the diamino alkanols and .the major portion of the organic acids, while the organic liquid stripped from the acids, contains a small portion of the diamino alkanol. By washing the stripped organic liquid with water, the diamino alkanol is re-extrac'ted by the latter. The aqueous solution so obtained may then be added to the caustic alkali solution containing the bulk of the diamino alkanol, and excess water may be separated from the result ing solution by distillation. I

More thorough extraction may be had, however, in a multistage countercurrent extraction system.

The amount of aqueous caustic alkali solution required in the extraction is normally above about by volume and for economical reasons seldom exceeds about 100% by volume. Normally from about to by volume are used depending upon the required thoroughness of removing the weak organic acids.

Spent aqueous caustic alkali solution containing the diamino alkanol and weak organic acids may be regenerated by distillation, steaming and/or oxidation, according to well known principles. I

' substances, and the other consisting essentially of the treated organic liquid and separating the layers.

2 The process of claim 1 in which the aqueous base solution contains between 15 and of the diamino alcohol.

3. The process of claim 1 in which the aqueous base is between 2 to 10% normal in the absence of the diamino alcohol. I

4. The process of claim 1 in which the hydrophobe liquid is extracted with 5 to volume percent .of aqueous base solution containing the diamino alcohol. i

5. The process of claim 1 in which the base is an alkali metal hydroxide.

6. The process of claim 1 in which the diamino alcohol is diaminoisopropanol.

'7. The process of claim 1 in which the diamino alcohol is diamino tertiary butanol.

8. In the process of separating mercaptans from hydrocarbon distillates containing same by extraction with an aqueous solution of caustic alkali, the improvement comprising extracting" said distillate with at least 5 volume percent of a 2 to 10 normal aqueous alkali metal hydroxide solution in which is dissolved between 15 and 85% of an aliphatic diamino alcohol having from 3 to 5 carbon atoms under conditions to absorb at least a major portion of the mercaptans in the aqueous solution and to 'form two layers, one comprising the aqueous alkali metal hydroxide solution containing substantially all of the diamino alcohol and the major portion of the mercaptans, and the other consisting essentially of treated hydrocarbon distillate, and separating the layers.

DAVID LOUIS YABROFF. 

